It is well known that peroxygen bleaches are effective for removing stains and/or soils, as well as visible evidence of stains and soils, from textiles and fabrics. Unlike sodium hypochlorite bleaching solution, they can be readily employed in a variety of bleaching and detergent compositions. However, the efficacy of peroxygen bleaches can vary greatly with temperature. These bleaches are only practicable and/or effective when the bleaching solution (bleach and water mixture) is above about 60.degree. C. When employed in a bleach solution at a temperature of about 60.degree. C., or below, peroxygen bleaches are significantly less efficacious than at higher temperatures. Therefore, to obtain a desirable level of bleaching performance at these lower temperatures, extremely high levels of peroxygen bleach must be employed. Due to the cost of peroxygen bleach compounds, levels necessary to achieve good bleaching performance at such temperatures are not economically attractive. In bleach solutions where the temperature is well below 60.degree. C., peroxygen bleaches are rendered almost totally ineffective regardless of the level of peroxygen bleach compound added to the system.
The dependence of peroxygen bleach performance on temperature and concentration described above is both practically and economically significant. Peroxygen bleaches are most commonly used as detergent adjuvants in home laundry products. Thus, the typical textile wash process employing these bleaches uses an automatic household washing machine and a wash-water temperature below 60.degree. C. Hand-washing is conducted at even lower temperatures, typically less than about 35.degree. C. As a consequence, there has been considerable interest in developing substances that would increase the efficacy of peroxygen bleach compounds, thereby allowing them to be employed at temperatures below 60.degree. C. Such substances are generally referred to in the art as "bleach activators" or "peroxygen bleach activators".
Most of these prior art bleach activators are solids and are intended primarily as adjuncts to conventional laundry detergent granules. Such laundry granules typically comprise a solid bleach activator in admixture with a coating or carder material which serves to enhance the stability of the bleach activator and to facilitate its uniform dispersion in the granular detergent.
Different from the solid bleach activators known heretofore, one class of bleach activators which have now been found to provide good bleaching of textiles lo and fabrics, especially on hydrophobic stains, comprise the liquid acyl lactam bleach activators, such as octanoyl caprolactam, octanoyl valerolactam, nonanoyl caprolactam and nonanoyl valerolactam. However, such substantially water-insoluble liquid lactam bleach activators can be difficult to use in granular laundry detergent compositions because they are liquids at ambient temperatures and tend not to solubilize/disperse satisfactorily in the wash water. Indeed, the unsolubilized liquid bleach activators can separate from the wash liquor as an oily liquid and fail to be converted to peracids, or can even ultimately cling to the fabrics in the wash where they react with the peroxygen bleach and spot or remove color from the fabrics.
According to the practice of the present invention, a surfactant intimately mixed with the liquid bleach activator would seem to solve the solubility/dispersibility problems. However, the liquid activators also need to be converted into a solid form which can be incorporated into granular detergent compositions. Because of the problems associated with converting a liquid bleach activator to a solid particle, the choice of a suitable surfactant is limited. It has now also been discovered that certain preferred surfactants help to thicken the liquid bleach activators into a non-sticky mass which can then be formed into particles while avoiding the tendency of the particles to "cake". Preferred surfactants and mixtures of surfactants have now also been found which provide good solubility of the otherwise poorly soluble activator once the particle is introduced into the wash liquor.
Accordingly, the present invention resolves the problems of utilizing liquid acyl lactam bleach activators in granule form by providing a stable matrix of materials in a particulate form that has satisfactory solution/dispersibility characteristics. The invention also provides non-sticky, free flowing bleach activator particles which are stable on storage even at temperatures of 50.degree.-55.degree. C., and higher. These and other advantages are provided by the instant invention, as will be seen from the following disclosure.